1. Field of the Invention
The present invention relates to a fluid-filled elastic mount such as an engine mount for a motor vehicle, and more particularly to improvements in such a fluid-filled elastic mount which is highly capable of damping low-frequency, large-amplitude vibrations, and isolating high-frequency, small-amplitude vibrations.
2. Discussion of the Prior Art
An elastic mounting device such as a mount for elastically mounting an engine on a motor vehicle is generally required to exhibit not only an excellent vibration-damping characteristic for vibrations having a comparatively low frequency and a comparatively large amplitude, but also an excellent vibration-isolating characteristic for vibrations having a comparatively high frequency and a comparatively small amplitude. As an elastic mount which satisfies these two requirements, a so-called fluid-filled elastic mount is proposed according to laid-open Publication No. 57-9340 (published in 1982) of unexamined Japanese patent application corresponding to German patent application No. 3019337.4. This fluid-filled elastic mount has (a) a first and a second support member which are spaced apart from each other by a suitable distance, (b) an elastic body disposed between the first and second support members for elastically connecting these two support members, (c) a closure member which is supported by the second support member and which cooperates with the second support member and the elastic body to define a fluid chamber which is filled with a suitable non-compressible fluid, at least a portion of the closure member being formed of a flexible material, (d) a partition member which is supported by the second support member and which divides the fluid chamber into a pressure-receiving chamber on the side of the elastic body and an equilibrium chamber on the side of the closure member, (e) a restrictor passage formed for restricted fluid communication between the pressure-receiving chamber and the equilibrium chamber, and (f) a movable member which is deformable or displaceable by a suitable amount in a direction so as to absorb a pressure difference between the pressure-receiving and equilibrium chambers.
The fluid-filled elastic mount constructed as described above is capable of effectively damping low-frequency large-amplitude vibrations based on flows of the fluid through the restrictor passage, and at the same time capable of effectively isolating high-frequency small-amplitude vibrations based on deformation or displacement of the movable member. That is, this type of elastic mount has excellent vibration damping and isolating characteristics.
In the known fluid-filled elastic mount constructed as described above, the movable member is generally supported by the partition member which consists of a metallic structure, as disclosed in the above-identified document. This type of partition member is difficult to manufacture and assemble, and the production efficiency of the elastic mount is accordingly low.
It is considered to use an integrally formed partition member made of a suitable elastic material so that a portion of the partition member is deformable in a direction so as to absorb or accommodate a pressure difference between the pressure-receiving and equilibrium chambers, in the fluid-filled elastic mount which has the above-indicated elements: first and second support members; elastic body; closure member; partition member; and means for defining a restrictor passage.
The above modified form of the fluid-filled elastic mount which uses the elastic partition member is capable of effectively isolating high-frequency small-amplitude vibrations based on deformation of the appropriate portion of the partition member so as to absorb the pressure difference. Hence, this elastic mount has substantially the same vibration damping and isolating characteristics as the fluid-filled elastic mount which uses a separate movable member as described above. The integrally formed elastic partition member is easier to produce and assemble, than the partition member which movably supports the movable member. Accordingly, the production efficiency of the elastic mount using the elastic partition member is significantly improved.
Although the elastic mount which uses the elastic partition member enjoys a comparatively high degree of manufacturing efficiency, it is difficult to provide the elastic mount with vibration-damping capability based on resonance of the fluid mass in the restrictor passage, as well as vibration-isolating capability based on deformation of the partition member, in the case where the restrictor passage is defined by a groove formed in the partition member so that the construction of the elastic mount is simplified.
Described more specifically, the integrally formed partition member made of an elastic material is generally secured or fixed at its outer portion to the second support member such that the outer portion is held in pressed contact with the inner surface of the second support member. The outer portion of the partition member has a groove open in its outer surface. The restrictor passage is defined such that the opening of the groove is closed by the inner surface of the second support member. While this arrangement simplifies the overall construction of the elastic mount, the arrangement suffers from operational drawbacks. Namely, if the partition member is formed of an elastic material having a relatively small modulus of elasticity so that the partition member is sufficiently deformable to provide an excellent vibration-isolating effect, the restrictor passage tends to have a considerably large variation or change in the cross sectional area, which causes an undesirable change in the frequency range of the vibrations that can be damped based on resonance of the fluid mass in the restrictor passage. If the partition member is formed of an elastic material having a relatively large modulus of elasticity to permit the restrictor passage to provide an excellent vibration-damping effect, on the other hand, the amount of deformation of the partition member is limited, and the vibration-isolating effect of the partition member is accordingly lowered.